This proposal will examine the relationship of the extent and type of pathogenesis by herpes simplex virus (HSV) with the efficiency of viral replication and transactivation of different viral strains isolated from sexually transmitted disease patients. HSV is one of the most common human pathogens that is found worldwide, with humans as the only natural reservoir. In the United States this is one of the most common sexually transmitted diseases. The relationship between the severity of viral infection, replication and transactivation (that may control expression of crucial replication genes) efficiencies has not been investigated at a molecular level. Preliminary experimental results from this laboratory indicate that different laboratory strains of HSV can replicate utilizing different lengths of a unique origin of replication and can transactivate homologous and heterologous promoters to dramatically different extents. A major part of our project involves basic research on expression of one out of seven virus-coded replication genes essential for viral DNA replication. This study will enable us in the future to target the expression of replication genes for antivirals that will block viral replication on a general (i.e. mostly strain variation independent) basis. The information to be obtained from the proposed study will give input to the behavioral, clinical and outreach components of this center to investigate the relationship between the sexual behavior of the patients, extent of disease, recurrence of HSV infection, possible co-infection with other STD agents, opportunistic infections by HSV in immunosuppressed patients and possible helper function of HSV infection with other STD agents. The specific aims of this proposal are: (1) To determine the replication efficiency of HSV strains purified from different clinical isolates from STD patients using an in vivo DNA replication assay. (2) To determine the transactivation efficiency of different clinical HSV strains from STD patients by performing transient transfection experiments with homologous and heterologous promoters in the presence and absence of the virus. (3) To study the expression of a HSV gene (UL-5), required for viral DNA replication and analyze its promoter and other transcriptional modules. The expression of this gene may serve as a specific target for antiviral drug.